Although alternating current provides important economies for transmission and distribution of power over significant distances and developing desired voltages proximate to the location where power is to be consumed, direct current (DC) at a desired, substantially constant and often closely regulated voltage is required by most electronic devices other than motors and illumination arrangements. While so-called analog regulators having a variable resistance in the series current path have been used in the past, switching power supplies and regulators avoid most of the power consumption involved in obtaining a desired voltage from an AC or unregulated DC source and many switching power supply and regulator topologies have been developed or are foreseeable. The reduction in power consumption is due to the fact that very little power is dissipated by the switches in their conductive or non-conductive states but only during the very brief periods during transitions between those states which are desirably as short as possible. On the other hand, for a given transition duration of the switches, the component of power consumption referred to as switching losses increases with switching frequency and imposes a trade-off between, for example, power consumption and load transient response time; favoring very short switching state transition times.
So-called wide bandgap switching devices have recently become available commercially which provide substantially improved switching performance over silicon transistor technologies. Specifically, increased electron saturation velocity, electron mobility, critical electric field for breakdown, bandgap energy and thermal conductivity are all achieved to some degree and in some cases by a substantial factor in gallium nitride (GaN) and silicon carbide (SiC) transistor technologies which lead to increased switching frequency, low on-state losses, high voltage capability and high temperature operation. In particular, switching devices made from these materials may exhibit switching transition times (e.g. dV/dt or slew rate during switching state transitions) several orders of magnitude larger than silicon switching devices. However, as a practical matter, the actual performance of wide bandgap semiconductor switches in power supplies and modules is often limited by the packaging and construction of the power module itself and the greatly increased electrical performance may substantially exacerbate problems normally associated with switching power converters.
Specifically, the high slew rate, dV/dt, exhibited by SiC and GaN devices can cause significant increases in electromagnetic interference (EMI) noise and common mode (CM) noise currents (I=C(dV/dt)) in parasitic capacitances (e.g. to a heat sink which is typically grounded for safety) in particular, especially at high frequencies which are difficult to filter. In fact, peak-to-peak noise currents can be comparable to the inductor current in the power module which can be conducted through electrical circuits and/or radiated as electrical fields that can induce voltages and/or currents in other circuits such as control and logic-level circuits with unpredictable results. While a combination of filtering and shielding of the entire power module is often used to reduce the lower CM EMI currents resulting from silicon switches to sufficiently low levels, such expedients are not adequate for the higher CM EMI currents resulting from SiC and GaN switches.